We are what we eat, right? But determining just what top marine predators consume has been a challenge for marine biologists and something of a Holy Grail in marine ecology. Cue the quest by Australian and Spanish scientists who are one step closer to finding the true diet of marine predators by combining two state-of-the-art techniques –stable isotope and DNA analysis.

“If we’re only examining scat or stomach contents we’re essentially only looking at an animal’s diet from the last 24 hours. Some foods are highly digestible and therefore not present or unidentifiable in such analyses and may therefore not reflect the true, long-term diet of a species.”

To form a more complete picture, Dr Chiaradia and Spanish researchers combined two rigorous techniques, stable isotope and DNA analysis, to study the diet of little penguins at Phillip Island, Australia. The research was the first time the two techniques were merged in one diet study. Their results, published this week in the online scientific journal PLOS ONE, showed surprising results.

“DNA analysis of scat provides a comprehensive list of prey species digested, while stable isotope analysis reveals what elements of a diet have been assimilated into the blood stream. Either one or the other technique is typically used in diet analysis, but rarely both,” Dr Chiaradia explains.

“We used a controlled, known diet for a group of penguins that were already in care at the Wildlife Clinic at Phillip Island Nature Parks.

“DNA scat analysis of penguins on that diet revealed different results to the stable isotope analysis, suggesting that the independent use of each technique will reveal different aspects of a diet. When we merged the two techniques in this novel way, the final output was the closest match to the controlled (true) diet.”

The results have important implications for Phillip Island’s little penguins and for the team of researchers at Phillip Island Nature Parks whose knowledge underpins conservation management decisions.

About Phillip Island Nature Parks:Phillip Island Nature Parks has been conducting little penguin research for over 43 years. With an estimated colony size of 32,000 breeding penguins on the Summerland Peninsula of Phillip Island, the not-for-profit organisation is committed to investing revenue from ecotourism into conservation, research and education programs. The research was also funded by grants from the Penguin Foundation (Australia), Junta Andalucia (Spain), European Union Research Fund and Ministerio de Educación y Ciencia de España.